Vertical photodiode

Abstract

Embodiments of this disclosure relate to a vertical photodiode. The vertical photodiode includes an active region. Contact pads for diode terminals are laterally shifted away from the active region so as not to be located above or below it. The active region is formed in a semiconductor material layer by an intrinsic lower portion of a germanium region and an upper portion of the germanium region doped with a first conductivity type. The vertical photodiode is optically coupled to a waveguide formed in the semiconductor material layer.

Description

[0001] Divisional Application Instructions

[0002] This application is a divisional application of Chinese invention patent application No. 201910169544.3, filed on March 6, 2019, entitled "Vertical Photodiode". Technical Field

[0003] This disclosure relates to photonics, and more specifically to optical-to-electrical signal converters or photoelectric converters. Background Technology

[0004] Optical fiber enables data to be transmitted in the form of optical signals, which are then converted into electrical signals.

[0005] The speed of data transmission through optical fiber is limited by the electro-optical converter (a modulator of an optical carrier by an electrical signal) and the photoelectric converter (a demodulator or photodetector) located upstream and downstream of the optical fiber, respectively. Summary of the Invention

[0006] One embodiment provides a vertical photodiode that includes an active region, all of which have contact areas shifted above the active region.

[0007] According to one embodiment, the active region is formed by an intrinsic lower portion of the germanium region and a doped upper portion of the germanium region having a first conductivity type, and the active region is formed in a semiconductor material layer.

[0008] According to one embodiment, the lateral wall of the upper portion of the germanium region contacts a first doped region of a first conductivity type, the first region extending above the upper surface of the semiconductor material layer.

[0009] According to one embodiment, the lower portion of the germanium region is in contact with a second doped region of a second conductivity type, the second region extending to the upper surface of the semiconductor material layer.

[0010] According to one embodiment, the contact area is located on a first region and a second region, which are preferably made of silicon.

[0011] According to one embodiment, the second region is partially made of SiGe.

[0012] According to one embodiment, the first region and the second region each extend on one side of the intrinsic germanium region.

[0013] According to one embodiment, the insulating trench is at least partially in contact with the first lateral surface of the germanium region.

[0014] According to one embodiment, the portion of the first lateral surface that does not contact the insulating trench is in contact with intrinsic silicon.

[0015] According to one embodiment, the potential difference between the contact areas of a photodiode represents the number of photons in the active region.

[0016] One embodiment provides a photoelectric converter that includes a photodiode such as those previously described.

[0017] According to one embodiment, the converter includes a waveguide.

[0018] One embodiment provides a method for manufacturing a vertical photodiode, wherein all contact areas are shifted above the active area.

[0019] According to one embodiment, the method includes the following steps: opening a cavity in the upper surface of a semiconductor material (preferably silicon) layer; doping the semiconductor material layer to form a first doped region of a first conductivity type that contacts the lateral walls of the cavity, and a second doped region of a second conductivity type that contacts the bottom of the cavity and extends to the surface of the semiconductor material layer; forming intrinsic germanium in the cavity; and an upper portion of the intrinsic germanium doped with the first conductivity type that contacts the first region.

[0020] According to one embodiment, the contact area is formed on the first region and the second region.

[0021] According to one embodiment, the method includes the step of forming an insulating trench that extends parallel to the active region.

[0022] According to one embodiment, the cavity is opened such that one side of the cavity is at least partially formed by an insulating trench.

[0023] According to one embodiment, the cavity is opened such that three sides of the cavity region are at least partially in contact with silicon. Attached Figure Description

[0024] The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments, taken in conjunction with the accompanying drawings, in which:

[0025] Figure 1A This is a top view illustrating one embodiment of an optical-to-electrical signal converter;

[0026] Figure 1B and Figure 1C They are along Figure 1A plane BB and along Figure 1A A cross-sectional view of plane CC;

[0027] Figures 2A to 2C It is a diagram. Figures 1A to 1C A cross-sectional view of the manufacturing steps of the embodiment; and

[0028] Figure 3 This is a cross-sectional view illustrating another embodiment of an optical-to-electrical signal converter. Detailed Implementation

[0029] In the various figures, the same elements are denoted by the same reference numerals, and the figures are not drawn to scale. For clarity, only those steps and elements useful for understanding the described embodiments are shown and described in detail.

[0030] In the following description, when terms such as “front,” “back,” “top,” “bottom,” “left,” and “right” modify absolute position, or terms such as “above,” “below,” “up,” and “down” modify relative position, or terms such as “horizontal” and “vertical” modify direction, refer to the orientation of the relevant element in the figure. The terms “about,” “approximately,” “substantially,” and “the magnitude of…” are used herein to indicate a tolerance of plus or minus 10% (preferably plus or minus 5%) of the value under discussion.

[0031] Figure 1A , Figure 1B and Figure 1C These are top views of one embodiment of the optical-to-electrical signal converter 10, along... Figure 1A The cross-sectional view of plane BB, and along Figure 1A A cross-sectional view of plane CC.

[0032] Converter 10 receives an optical signal from optical fiber 14 at input 12. Optical fiber 14 and converter 10 can be separated, for example, by optical circuitry with multiplexing capabilities or by a device capable of receiving and transmitting optical signals originating from the fiber. Converter 10 includes a substrate (not shown), for example, made of silicon. The substrate is covered with an insulating layer 16 (…). Figure 1B and Figure 1C Layer 16 is covered with a semiconductor material (preferably silicon) layer 18. Layer 18 is covered with an insulating layer 24. Figure 1A (Not shown in the image).

[0033] The transducer includes a waveguide shaft 17. The waveguide 17 includes two trenches 20a and 20b filled with insulator formed in layer 18. Trenches 20a and 20b define a region 22 located between the two trenches 20a and 20b. Figure 1A and Figure 1C ), and in the surrounding area 23. Each trench 20a and trench 20b is located between areas 22 and 23. The height of trench 20a and trench 20b is less than the thickness of layer 18.

[0034] Region 22 of waveguide 17, horizontally defined by trenches 20a and 20b and vertically defined by layers 16 and 24. Figure 1A This forms the region in which the optical signal propagates. In fact, silicon is transparent to the wavelength in question, and the insulators of trenches 20a and 20b, as well as layers 16 and 24, are chosen to have a refractive index sufficiently different from that of silicon to contain the optical signal. For example, trenches 20a and 20b, as well as layers 16 and 24, are made of silicon dioxide with a refractive index of 1.45, while the refractive index of silicon is 3.5.

[0035] The converter 10 also includes a vertical photodiode 26 ( Figure 1A and Figure 1B A vertical photodiode is a photodiode whose active region is connected to the contact region via its upper and lower surfaces and conductive or semiconductor material.

[0036] Photodiode 26 is included in the path of the optical signal and in region 22 ( Figure 1A The germanium region 28 is relatively positioned. Therefore, region 28 is an extension of region 22. Region 28, for example, has a substantially parallelepiped shape. Figure 1B As shown, region 28 includes the lower intrinsic germanium portion 30 (Ge(i)) and the upper doped germanium portion 32 (Ge(P)). Figure 1A , Figure 1B and Figure 1C In the example, the germanium in the upper portion 32 is P-type doped. The lower portion 30 forms the active region of the photodiode 26.

[0037] Trench 20b extends parallel to region 28. Trench 20a extends only in waveguide 17 and not at the level of the photodiode.

[0038] exist Figure 1B In the cross-section shown, the upper surface of region 28 contacts the insulating layer 24, and the other three surfaces contact the silicon of layer 18. One of the lateral surfaces ( Figure 1B The region 34 (Si(i)) is separated from the trench 20b by the intrinsic silicon region 34. The trench 20b separates region 34 from the silicon region 36 (Si(N+)) which has a doping type opposite to that of the upper portion 32. In this example, region 36 is N-type doped. Region 36 is an extension of region 23 in waveguide 17. The lower surface of region 28 contacts region 38 (Si(N)), which separates region 28 from layer 16 and extends from region 28 to region 36. Region 38 has the same doping type as region 36 (N in this case) and is, for example, lightly doped than region 36. The other lateral surface of region 28 (in Figure 1BOn the right-hand side (upper), the lower portion 30 contacts the intrinsic silicon region 40 (Si(i)) at the layer level, and the upper portion 32 contacts the doped silicon region 42 (Si(P+)) at the layer level, the doped silicon region 42 having the same conductivity type as the upper portion 32 (here, P). Region 42 is, for example, more heavily doped than the upper portion 32. Region 42 extends above the surface of layer 18, and more specifically above region 40.

[0039] The doping concentration of the upper portion 32 is, for example, from about 10 18 cm -3 To about 10 19 cm -3 Within the range. The doping concentrations in regions 36, 38, and 42 are, for example, from approximately 10... 18 cm -3 To about 10 20 cm -3 Within the range.

[0040] The contact areas of the photodiode are formed on regions 36 and 42. More specifically, contact pad 44 is formed on region 36, and contact pad 46 is formed on region 42. Vias 48 and 50 cross the insulating layer 24 to reach pads 44 and 46, respectively. Therefore, the contact areas of the photodiode are all laterally shifted from the active region 30 (i.e., not located above the active region 30).

[0041] Therefore, the lower surface of the active region 30 is electrically connected to the via 48 via an N-type doped semiconductor region (regions 36 and 38) extending to the surface of layer 18, and the upper surface of the active region 30 is electrically connected to the via 50 via a P-type doped semiconductor region (regions 32 and 42).

[0042] The optical signal supplied to input 12 by optical fiber 14 can propagate through waveguide 17 to photodiode 26, and more specifically to the lower portion 30 of region 28. Upon arrival of the optical signal, the underlying intrinsic germanium portion 30 generates charge carriers. Therefore, the voltage measured between region 36 and portion 32 (via vias 48 and 50) represents the data transmitted by the optical signal. More specifically, the potential difference between the contact areas of the photodiode represents the number of photons in the active region, and thus the optical signal arriving at the photodiode.

[0043] The refractive index difference between germanium (4.5) and intrinsic silicon (3.5) is sufficient to confine the signal within the active region for the time required to transmit the message.

[0044] As a variation, the lower portion 30 of region 28 can be separated from region 38 by being doped with a silicon-germanium layer (SiGe) (not shown) of the same conductivity type as region 38 (here, N).

[0045] For example, in Zone 28 Figure 1B The cross-sectional plane has a width ranging from about 500 nm to about 1200 nm (preferably from 500 nm to 1200 nm). The intrinsic germanium portion 30 has a thickness, for example, ranging from about 150 nm to about 500 nm (preferably from 150 nm to 500 nm). The doped germanium portion 32 above has a thickness, for example, ranging from about 50 nm to about 100 nm (preferably from 50 nm to 200 nm). Trench 20b in Figure 1B The cross-sectional plane has a width, for example, ranging from about 400 nm to about 800 nm (preferably, from 600 nm to 800 nm). The region 28 and the contact pad 46 are spaced apart by a distance, for example, ranging from about 400 nm to about 800 nm (preferably, from 400 nm to 800 nm).

[0046] Contact pads 46 and vias 50 can be formed directly on the upper portion 32 of region 28. However, manufacturing inaccuracies may result in the formation of vias 50 that partially extend within portion 32. The portion of via 50 extending within the germanium of portion 32 will absorb a portion of the optical signal (which will then be lost). Additionally, fabricating pads on two different materials imposes limitations in terms of manufacturing processes.

[0047] Figures 1A to 1C The advantage of this embodiment is that inaccurate manufacturing at the via 50 level may result in via 50 extending at most up to region 42 (without extending into region 28). Therefore, via 50 will not be in the path of the optical signal.

[0048] Figures 2A to 2C It is a diagram. Figure 1A and Figure 1B A cross-sectional view of the manufacturing steps of an embodiment.

[0049] Figure 2A The manufacturing steps are illustrated. During this step, an insulating layer 16 is formed on a substrate (not shown). Then, a semiconductor material layer 18, preferably made of intrinsic silicon, is formed on layer 16. Trench 20a and trench 20b are formed in layer 18. Trench 20b extends over the entire photoelectric converter 10 (waveguide and photodiode), and trench 20a (in...) Figures 2A to 2C (Not shown) extends all the way to the location where the photodiode will be formed. Therefore, the waveguide in which the optical signal will propagate from the optical fiber to the photodiode is formed between trench 20a and trench 20b. Figure 2A The plane of the cross-section is located in the portion where the photodiode will be located. Therefore, only trench 20b is shown.

[0050] Figure 2AThe trench 20b shown separates region 52 from region 36. Region 52 is located on the surface of the end of the waveguide (not shown).

[0051] Then, a doping operation is performed. Specifically, region 36 is N-type doped (N+), and region 38, located below region 52, below trench 20b, and below region 36, is also N-type doped. Region 38 is lightly doped compared to region 36. Located at the surface of layer 18 and from the periphery of layer 18 ( Figure 2A Region 42, which extends from the right-hand side of region 52 and partially extends above region 52, is P-type doped (P+).

[0052] Then, contact pads 44 and 46 are formed on regions 36 and 42, respectively.

[0053] An insulating layer 54 is deposited on the described structure to fill trenches 20a and 20b and cover layer 18, as well as pads 44 and 46. Layer 54 is made of, for example, the same insulating material as layer 16, such as silicon dioxide.

[0054] Figure 2B The diagram illustrates the subsequent manufacturing steps. During this step, cavity 56 is formed in layer 54 and region 52.

[0055] Cavity 56 is deep enough that its bottom lies within region 38. Furthermore, cavity 56 is positioned such that region 42 forms part of the transverse wall of cavity 56. Figures 2A to 2C In the example, cavity 56 is positioned in such a way that intrinsic silicon region 34 separates the cavity from trench 20b.

[0056] Figure 2C The subsequent manufacturing steps are illustrated. During this step, germanium is formed in cavity 56 by epitaxial growth to form region 28, thereby completely filling the portion of cavity 56 located in layer 18. Germanium may optionally fill the entire cavity 56. Figure 2C In the cross-sectional plane, germanium is formed on three walls.

[0057] Then, the upper portion 32 of region 28 is p-type doped. The lower intrinsic portion 30 forms the active region.

[0058] The structure is then covered again with an insulator to form layer 24 as described previously, the insulator being, for example, the same insulator as layer 16 (e.g., silicon dioxide).

[0059] During subsequent steps (not shown), vias 48 and 50 are formed as through layer 24.

[0060] As a variation, there may also be a step of forming an N-type doped SiGe layer at the bottom of cavity 56 (not shown).

[0061] Figure 3 This is a cross-sectional view illustrating another embodiment of an optical signal to electrical signal converter. In this embodiment, the cavity 56 is excavated in such a way that one wall of the cavity is partially formed by a trench 20b. Furthermore, the height of the trench 20b is lower than... Figures 2A to 2C The height of the groove 20b in the embodiment.

[0062] Therefore, the wall of the active region 30 located on one side of the trench 20b partially contacts the trench 20b and partially contacts region 58. Region 58 is made of the material of layer 18, preferably intrinsic silicon. Region 58 has a lower height compared to the height of germanium region 28.

[0063] As a variation, trench 20b can have a thickness greater than the height of silicon region 28. Therefore, the wall of region 28 located on one side of trench 20b will be in complete contact with trench 20b. Thus, in Figure 3 In the cross-sectional plane, germanium in region 28 will only form on the two walls.

[0064] During the epitaxial growth step, with Figure 1B Compared to the previous embodiment, in the two walls of cavity 56 (in) Figure 3 The formation of small heights of germanium in the cross-sectional plane (and possibly in region 58) allows for a reduction in the number of dislocations in germanium (leading to losses at the level of the transmitted signal). However, the growth of germanium is more... Figure 1B The embodiments are longer.

[0065] The frequency of converter 10 depends on the resistance between the active region and the contact region, as well as the capacity of the active region between region 38 (N-doped) and region 32 (P-doped). The lower the capacity and resistance, the higher the frequency.

[0066] The advantage of this embodiment is that the active region can have a small thickness and therefore a small capacitance, while maintaining sufficient width to allow dislocations formed during the epitaxial growth of germanium to be located around region 28. Therefore, the frequency of this converter can be increased relative to conventional converters, which allows for an increase in flow rate relative to current technology that allows for transmission speeds of approximately 25 Gbps (gigabits per second).

[0067] The height of trench 20b is, for example, in the range of about half the thickness of layer 18 to about five-sixths of the thickness of layer 18. The thickness of layer 18 is, for example, about 300 nm, preferably 300 nm, and the height of trench 20b is, for example, in the range of about 50 nm to about 150 nm, preferably in the range of 50 nm to 150 nm.

[0068] The choice of trench 20b depth allows for modification of the resistance between some contact areas in the active and contact regions, which in turn allows for modification of the converter frequency.

[0069] Specific embodiments have been described. Various changes, modifications, and improvements will be readily apparent to those skilled in the art. Specifically, the P and N conductivity types can be interchanged.

[0070] As a specific embodiment, the described converter is suitable for optical signals, for example, having a wavelength of 1310 nm or 1550 nm.

[0071] Various embodiments with different variations have been described above. It should be noted that those skilled in the art can combine various elements of these various embodiments and variations without showing any inventive steps.

[0072] Such changes, modifications, and improvements are intended to be part of this disclosure and are intended to fall within the spirit and scope of the invention. Therefore, the foregoing description is merely exemplary and not intended to be limiting. The invention is limited only by the claims and their equivalents.

Claims

1. A vertical photodiode, comprising: Semiconductor material layer, having an upper surface; An insulating trench extends from the upper surface into the semiconductor material layer; An active region is located within the semiconductor material layer on a first side of the insulating trench. The active region includes a diode formed by: a germanium region including an intrinsic lower portion and an upper portion doped with a first conductivity type, and a doped region of a second conductivity type, wherein the doped region of the second conductivity type is made of silicon or the doped region of the second conductivity type is at least partially made of silicon and germanium. The doped region of the second conductivity type extends below the insulating trench; The first doped contact region of the first conductivity type laterally contacts the upper portion of the germanium region, and the first doped contact region extends above the upper surface of the semiconductor material layer; The first contact pad is positioned to contact the first doped contact region; The second doped contact region of the second conductivity type contacts the doped region of the second conductivity type, and the second doped contact region extends on the second side of the trench opposite to the first side; as well as The second contact pad is positioned to contact the second doped contact region on the upper surface of the semiconductor material layer.

2. The photodiode according to claim 1, wherein there is a portion of the first doped contact region that does not contact the first contact pad between the upper portion of the germanium region and the first contact pad.

3. The photodiode according to claim 1, wherein the first doped contact region and the second doped contact region are made of silicon.

4. The photodiode of claim 1, wherein the second doped contact region is at least partially made of silicon-germanium.

5. The photodiode of claim 1, wherein the depth of the insulating trench is below the bottom of the lower portion of the germanium region.

6. The photodiode of claim 1 further includes an intrinsic silicon region located between the germanium region and the first side of the insulating trench.

7. The photodiode of claim 1, further comprising an intrinsic silicon region in contact with both the lower portion of the germanium region and the doped region of the second conductivity type.

8. A vertical photodiode, comprising: An active region is formed in a semiconductor material layer, wherein the active region includes a diode formed of: an intrinsic lower portion of a germanium region, an upper portion of the germanium region doped with a first conductivity type, and a second doped region of a second conductivity type located in the semiconductor material layer, wherein the second doped region is in contact with the lower portion of the germanium region, and the second doped region is made of silicon or the second doped region is partially made of silicon and germanium. A first doped region of the first conductivity type is located in the semiconductor material layer, wherein the first doped region is in contact with the lateral wall of the upper portion of the germanium region; A first contact pad and a second contact pad are electrically coupled to the diode, wherein the first contact pad and the second contact pad are located at a position laterally offset from the active region, the first contact pad is positioned to contact the upper surface of the first doped region, and the second contact pad is positioned to contact the upper surface of the second doped region. An insulating trench separates the active region from the second contact pad; as well as The intrinsic silicon region is located between the active region and the insulating trench.

9. The photodiode of claim 8, wherein the portion of the first doped region not covered by the first contact pad is located between the active region and the first contact pad.

10. The photodiode of claim 8, wherein the first doped region is made of silicon.

11. The photodiode of claim 8, wherein the second doped region includes a portion located on the side of the intrinsic germanium region opposite to the first doped region.

12. The photodiode of claim 8, wherein the potential difference between the first contact pad and the second contact pad represents the number of photons in the active region.

13. A photoelectric converter comprising a vertical photodiode according to any one of claims 8 to 12.

14. The converter of claim 13, further comprising an optical waveguide coupled to the vertical photodiode.

15. A method for manufacturing a vertical photodiode, comprising: A pair of parallel insulating trenches are formed in a semiconductor material layer, wherein a first region of the semiconductor material layer between the parallel insulating trenches forms an optical waveguide, and wherein a second region of the semiconductor material layer is defined to be adjacent to one of the trenches in the pair of parallel insulating trenches. The semiconductor material layer doped in the second region forms a first doped region of a first conductivity type, wherein the first doped region is located on the upper surface of the semiconductor material layer; The semiconductor material layer doped in the second region forms a second doped region of a second conductivity type opposite to the first conductivity type, wherein the second doped region is buried in the semiconductor material layer and extends below one of the trenches of the pair of parallel insulating trenches, wherein the second doped region forms a second conductivity type portion of a vertical photodiode configured to detect light propagating in the optical waveguide; A cavity is opened in the semiconductor material layer, wherein one side of the cavity is at least partially defined by the edge of the first doped region, and the bottom of the cavity is at least partially defined by the upper surface of the second doped region; The cavity was filled with intrinsic germanium; The upper portion of the intrinsic germanium doped in the cavity forms a third doped region of the first conductivity type, the third doped region being in contact with the first doped region, wherein the third doped region forms a first conductivity type portion of the vertical photodiode; The lower portion of the intrinsic germanium in the cavity is the intrinsic portion of the vertical photodiode.

16. The method for manufacturing a vertical photodiode according to claim 15, further comprising: A first contact region is formed on the first doped region; as well as A second contact region is formed on the second doped region; The first contact area and the second contact area provide electrical contact for the vertical photodiode.

17. The method of manufacturing a vertical photodiode according to claim 15, wherein opening the cavity comprises: The cavity is positioned on the other side of the cavity at a location at least partially defined by the insulating trench.

18. The method of manufacturing a vertical photodiode according to claim 17, wherein doping the semiconductor material layer to form the second doped region comprises: A portion of the semiconductor material layer that contacts the bottom of the insulating trench remains undoped.

19. The method of manufacturing a vertical photodiode according to claim 18, wherein the undoped portion of the semiconductor material layer is in contact with the intrinsic germanium in the cavity.

20. The method for manufacturing a vertical photodiode according to claim 15, wherein opening the cavity comprises: The cavity is positioned on a portion of the semiconductor material layer between the other side of the cavity and the insulating trench.

21. The method of manufacturing a vertical photodiode according to claim 20, wherein said portion of the semiconductor material layer is an intrinsic semiconductor material.

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